Off-Grid System with Grid back-up switch

[mauritsfpv]

Hello everyone,

I am flirting with the idea of installing a solar system for a friend of mine in Ocean View, Cape Town (South Africa). They experience load-shedding and hence regular blackouts. To counter this I want to install a small, 2-3KW system with battery backup, enough to go fully off grid because the feed-in tariff system over there doesn't really work (to my understanding..).

However, hypothetically speaking if something in the system goes down, and the house is not supplied by solar power anymore, I would like to still have the possibility to switch on the grid to supply electricity. I realize that this is what hybrid systems are, however, the current setup does not support connection with the grid.

So I was thinking about making a separate physical switch outside that either switches on the solar - battery system to supply the energy or switches off the solar system and opens the connection to the grid. This to separate the power from the grid and the solar system.

Are there schematics available for something like this? Or would this be overcomplicating things? Any suggestions on this matter?

Another thing, maybe in the future, through expanding the system, can the system be shared by neighbors with light loads in order not to waste any generated electricity, also while they would be still connected to the grid to supply the higher loads?

Attached is roughly the setup I had in mind. Any comments?

Thanks so much for the help!

Maurits

[neweclipse]

As for any wasted PV output, any extra HW tank storeage capacity can be another way to store any excess PV production...much like another battery.

Sensing excess production amount and then signaling diversion into HW storage tank for later use.

[Ampster]

I dont know what you mean when you say current setup?

Most quality hybrid inverters contain a transfer switch that connects the load panel to the grid and disconnects the grid then connects that panel to the inverter when the grid is down. Your diagram does not show that nor does it show where the existing grid connection is. A manual transfer switch is possible but you should consult your Authority Having Jurisdiction for what is required. There are a number of electrical paths but only a few that are safe, workable or allowed in your country.

[mauritsfpv]

A hot water system is most probably not feasible unfortunately.. Good idea though.

Yes, maybe i should upgrade to a proper hybrid inverter. The current one is for a complete off grid system.

Any inputs on how a system of powersharing to neighbors could work? What kind of equipment would they need to accept the power in their house?

Thanks for the replies!

[jflorey2]

I am flirting with the idea of installing a solar system for a friend of mine in Ocean View, Cape Town (South Africa). They experience load-shedding and hence regular blackouts. To counter this I want to install a small, 2-3KW system with battery backup, enough to go fully off grid because the feed-in tariff system over there doesn't really work (to my understanding..).

However, hypothetically speaking if something in the system goes down, and the house is not supplied by solar power anymore, I would like to still have the possibility to switch on the grid to supply electricity. I realize that this is what hybrid systems are, however, the current setup does not support connection with the grid.

From the grid's perspective, the grid does not need "to support grid connection." When not in SELL mode, a hybrid inverter looks just like any other load.

1) Get a good hybrid inverter like the Radian.
2) Get a battery bank. Connect it.
3) The Radian takes the grid as an input. So connect that.
4) Wire the Radian's output to the home's load panel.
5) Commission the Radian.*

You are done.

Now if you want to add solar:

1) Get a good charge controller.
2) Install a solar array compatible with that charge controller.
3) Connect the output of the charge controller to the battery.
4) Configure the Radian to never export power and to use battery power preferentially.*

Now the solar panels will support the house load when the sun is out. If the load is lower than the solar output that power is lost. If you want to run an extension cord to someone else you can do that, then they can use that power too.

Also if you want to add a backup generator you can do that too. The Radian will handle all the switching for you.

(* - there are, of course, a great many more details than that. But them's the basics.)

[mauritsfpv]

This is valuable input, thank you!
I realize that a hybrid inverter is just the way to go, rather than fiddling with manual power switches.

Why would you want to add a backup generator? For situations where there is no backup grid?

Also, regarding the power-sharing idea, is there a way to create a system that sheds excess power to a neighbor automatically?

I imagine something like this: Once the charge controller fully charges the batteries, a signal is sent to an additional control unit at the neighbor that prefers power coming from the panels rather than power from the grid. If the batteries aren't fully charged yet, then power is not being sent to the neighbor.

This almost like the first baby steps towards forming a microgrid within a handful of households, where ultimately a blockchain system could facilitate microtransactions between solar arrays and battery storage to realize a prosumer micro power grid (that does not need to be connected to the main grid anymore).

That's the idea, but initially, I would just like to see if there are some control units out there that can help with automatic power-shedding to neighbors.

Thanks for all the input! I am new here, and this is really helpful!

Maurits

[jflorey2]

This is valuable input, thank you!
I realize that a hybrid inverter is just the way to go, rather than fiddling with manual power switches.

Why would you want to add a backup generator? For situations where there is no backup grid?

If you want 100% power availability. For infrequent/short outages not as important.

Also, regarding the power-sharing idea, is there a way to create a system that sheds excess power to a neighbor automatically?

You could use the charge controller or inverter to drive a relay based on battery voltage. The relay would enable power to the neighbor. If battery voltage is high share power. If battery voltage is low, do not. You might want to add a second relay wired for an AND function - if voltage is high AND solar is available, then share power.

This almost like the first baby steps towards forming a microgrid within a handful of households, where ultimately a blockchain system could facilitate microtransactions between solar arrays and battery storage to realize a prosumer micro power grid (that does not need to be connected to the main grid anymore).

That's a long way from that.

[neweclipse]

So then...this excess PV production wiould need to 'bypass' any neighbors grid meter? And at what distance...10 meter or half kilometer???

Getting PV power is like getting power from a tea cup...getting grid power is like getting power from the ocean...the leftover PV can be a dribble...

guess my point is that to help neighbors it is best to have a means to 'buffer' the dribble or in other words make battery storage at neighbors to catch and store all dribble...

[jflorey2]

So then...this excess PV production wiould need to 'bypass' any neighbors grid meter? And at what distance...10 meter or half kilometer???

It would be an extension cord that they could use for occasional power. It would be unreliable. It would not go through their meter. It would not be a "microgrid."

Getting PV power is like getting power from a tea cup...getting grid power is like getting power from the ocean...the leftover PV can be a dribble...

xactly

guess my point is that to help neighbors it is best to have a means to 'buffer' the dribble or in other words make battery storage at neighbors to catch and store all dribble...

OK.

[mauritsfpv]

Would you know any system that is available and could do the relay switching for this purpose? Or would it be something I d have to do myself?

Regarding the dribble factor I expect to produce roughly 30% too much energy. And also have roughly 30% overcapacity on my batteries. Feeding energy back into the grid will incur a fixed fee which makes it useless.

Therefore I wanted to explore other options for utilizing the energy that I won't.

So if I could program the relay such that it shares power once batteries reach a 70-80% charge, and then indeed somehow bypass the meter and only allow current to flow one way - to the neighbors- it would be possible right?

Length wise it would be max 10 meters.

Has this never been done before?

[Ampster]

I agree with jflorey2, an extension cord is the simplest. You could use a relay or switch to control when you want to share power with them. When they are connected the circuit that powers the extension cord will appear as one of your loads and be managed by your hybrid inverter. Anything more would involve a microgrid. There is nothing micro in term of expenses to install a microgrid. I was involved in planning one in a city in which all the city properties were contiguous. It was simpler because the user was the same entity and the Power Compny did not have to grant permission. At least that was the rule in California, USA. You will have to do some research for your jurisdiction to see what the rules are. It goes without saying that the City system I described above would be designed to comply with all building codes.

[mauritsfpv]

jflorey2 Ampster and also neweclipse thanks for the input. I really appreciate it. Just new here to get some perspective on thoughts and ideas.

As a quick intro, I have been involved with a few solar projects, both residential and larger utility-scale ones in California - but I am by no means an engineer, as you probably guessed already. However, why I keep on coming back to a microgrid style system - is because I believe its the future.
I am from the Netherlands where a grid-tied system is all you need, because of our favorable feed-in tariffs. A friend of mine is living in South Africa though and power outages and highly unfavorable feed-in tariffs make a hybrid system attractive (also pretty sunny with 1700-1900kwh/kwp versus +-900 kwh we get in NL). So far so good, relatively simple.

Now the idea of powersharing - between the community - tracked through microtransactions like the Brooklyn Project in NY (similar to your project Ampster ? What was it called?), is maybe a tiny bit on the optimistic side but it would be awesome to realize a baby version in his community in Ocean View CapeTown.

Therefore, starting with a slightly oversized hybrid system and shedding excess power to neighbors was my idea of creating a scalable prototype. He's got neighbors that are willing to pay him for supplied electricity matching existing rates. This creates the potential for him to also make some money - keeping money within the community. If this would work, this could hypothetically be copied by neighbors willing to make the investment. Energy consumption per household over there is roughly 3000kwh annually, so one roof can easily supply a couple of neighbors.

Long story short - that why I am looking for something that can work automatically instead of just running an extension cord.

Love to hear your thoughts on this idea.

[jflorey2]

Therefore, starting with a slightly oversized hybrid system and shedding excess power to neighbors was my idea of creating a scalable prototype. He's got neighbors that are willing to pay him for supplied electricity matching existing rates. This creates the potential for him to also make some money - keeping money within the community. If this would work, this could hypothetically be copied by neighbors willing to make the investment.

Sure. You could add a second feed to each home. You'd have to run lines (probably buried) and get a utility grade meter at the input. You'd need each person to then install something like a Radian + batteries to manage the power input. You could feed the generator input and limit power to some limit (1000W?) and program their Radian to use the generator input but limit its draw to 1000 watts - and switch back to the grid when needed. I'd guess about $20K per installation, and it will require a building permit and probably some work at the AHJ. Then you bill based on the second meter. That's the right way to do it.

I won't wait for your reply, which will probably be "WHAT? WAY too expensive!"

So it's back to the extension cord. Use a relay to turn it on when you have extra power. If you want to bill them get a cheapo energy meter. ($20 at Home Depot.) If you want them to have power at night too then have them buy a $99 UPS from Best Buy. Then plug the stuff that they don't rely on into the UPS.

[neweclipse]

Would you know any system that is available and could do the relay switching for this purpose? Or would it be something I d have to do myself?

Regarding the dribble factor I expect to produce roughly 30% too much energy. And also have roughly 30% overcapacity on my batteries. Feeding energy back into the grid will incur a fixed fee which makes it useless.

Therefore I wanted to explore other options for utilizing the energy that I won't.

So if I could program the relay such that it shares power once batteries reach a 70-80% charge, and then indeed somehow bypass the meter and only allow current to flow one way - to the neighbors- it would be possible right?

Length wise it would be max 10 meters.

Has this never been done before?

You should have a look at Midnite Classic Charge Controller...they have exactly what you are looking for.

[Ampster]

The City microgrid I spoke about is for a new Fire Station which that City has to build as part of its arrangement with the County, but the County will provide long term financing at favorable rates. They are talking about a micro grid because it will provide resilience using a combination of solar, batteries and a generator. It would power the Fire Station and provide emergency power for the police department for use in emergencies. It is still in the planning stage.